The invention relates to an unbalance correcting mechanism having rollable balls and a rolling groove to correct unbalance generating in a rotating device, and more specifically to a disk drive, such as CD-ROM and DVD-ROM drives, which reproduce information, or DVD-RAM, MO and removable HD drives, which write and read information, for rotating a disk-shaped, removable recording medium at high speed.
Japanese Patent Gazette No. 2,824,250 describes a balancer for correcting unbalance of a disk drive. The balancer comprises a hollow annular portion formed integral with a rotor and balancing members (spherical bodies) movable in the hollow annular portion. Japanese Patent Unexamined Publication No. H10-92094 describes a disk type storage device comprising at least one balance correcting weight freely movable on a path having a center of rotation, which coincides with that of a disk to automatically correct unbalance of the disk.
Japanese Patent Unexamined Publication No. H11-154371 describes a disk drive comprising a ring groove provided on a turntable with its center coinciding with a center of rotation and dynamic balance correcting balls movably received in the ring groove, thereby enabling substantially reducing vibrations and noises, and describes measures, such as application of a lubricant, for example, graphite, molybdenum disulfide, fluororesin and silicone oil, on a wall surface of the ring groove, or injection of a liquid into the ring groove, and formation of a hard layer of chromium plating inside the ring groove, for the purpose of dampening vibrations of the balance correcting balls.
Also, Japanese Patent Unexamined Publication No. H11-156243 describes a centrifugal separator for specimens, provided with a ball balancer, which is capable of suppressing noises caused by unbalance of a turntable and vibrations of the turntable and test tubes, and describes that surfaces of balls are covered with rubber or synthetic resin and surfaces of the ball balancer are applied with a coating agent, such as ethylene glycol, that has a high self-lubricating quality.
The above-described Patent No. 2,824,250 and Japanese Patent Unexamined Publication No. H10-92094 describe the structure, working principle and operation of the unbalance correcting mechanism. Basically, a balance member or a correcting member is moved in a hollow annular portion or in a rolling groove by a centrifugal force generated by unbalanced forces, whereby unbalance is corrected. In the above-mentioned prior art, balls are essentially used as the balance member or correcting member, and therefore an explanation will be given below collectively with respect to balls assuming that the a hollow annular portion or a rolling groove serves as a rolling groove.
In such an unbalance correcting mechanism, there is a fear that the balls and the rolling groove slidingly contact with each other as a disk drive is driven, and so fitting of contact portions proceeds to cause a change in correcting function. In order that a lubricating oil injected into a rolling groove at the time of assembly be diffused evenly over the entire rolling groove and correcting member, a preliminary operation of the correcting member in advance is necessary. In approximately 200 hours of preliminary operation, fitting of contact portions and diffusion of a lubricant are completed with the result that a stable unbalance correcting function can be obtained. Therefore, prior to shipment of a disk drive, running-in operation must be performed to complete the above fitting.
Time required for the running-in operation is a cause for an increase in cost, and so it is essential to shorten such time as much as possible.
Also, during running-in operation of a disk drive and operation of the disk drive after the running-in operation surfaces of balls and a rolling groove are scraped off to produce wear particles. These particles may get filled between the balls and the rolling groove to obstruct smooth movements of the correcting member and further make the balls immovable, which adversely affects reliability of the disk drive. It is thus essential to eliminate immovability the balls.
Further, a lubricating oil is injected into the rolling groove not only to reduce wear of the balls and the rolling groove but also to adjust the sliding quality of the balls. When an amount of the lubricating oil is too much, however, restraining forces on the balls and the rolling groove may become excessively great to cause immobility of the balls. conversely, when an amount of the lubricating oil is too little, restraining forces on the balls and the rolling groove may become excessively small to cause the balls to stray, so that the balls fail to stop relative to the rolling groove at the unbalance correcting position. It is a subject to prevent immobility and straying of the balls.
When a lubricant is injected as described in Japanese Patent Unexamined Publication No. H11-154371, it will take time for the injected lubricant to uniformly wet the balls and the ring groove, and so a preliminary operation is necessary. Also, the lubricant is easy to wet the balls, and the lubricant offers resistance to make it hard for the balls to roll. It is difficult to adjust friction between the balls. and the ring groove to a level not too large or too small. So, such adjustment imposes a problem. Also, it is another problem to adjust the hardness of the hard film formed in the ring groove to an optimum level.
Control of film thickness of rubber or synthetic resin described in Japanese Patent Unexamined Publication No. H11-156243 also imposes a problem in a high-density storage apparatus such as disk drives. Also, rubber having a thickness on the order of micron is liable to generate contamination due to wear. When ethylene glycol is added, it is problematic to optimize an amount added.
An object of the present invention is to provide a disk drive, which solves the above problems and which can reduce time for running-in operation to lower cost and prevent immobility and straying of balls.
The disk drive according to of the invention has the following structural features to solve the above-mentioned problems.
That is, the disk drive has an annular groove centered on an axis of rotation of a spindle motor, and a plurality of rollable correcting bodies provided in the annular groove, surfaces of the correcting members having surface tension of 30 dyne/cm or less and a contact angle of 80-150 degrees with respect to water. Thus surfaces of the correcting members are treated with polymer of fluoroalkylsilane or fluoroalkylsilane or with a layer of fluororesin.
Also, a lubricating oil, of which main component is ester oil, is injected into the annular groove.
Further, the annular groove is formed on a surface thereof with a hard film layer, which has a Vickers hardness of 600 or higher. In addition, the hard film layer is a plating layer containing nickel as its main component, phosphorus and boron.
Further, in order that upon application of centrifugal forces due to rotation of the spindle motor, a lubricating oil in the annular groove will not reach areas where the correcting members come into contact with the sidewall of the annular groove, a recess or a projection is provided between the bottom surface of the annular groove and that point on a sidewall of the annular groove, with which the correcting members are brought into contact.